The Class I HDAC Inhibitor, MS-275, Prevents Oxaliplatin-Induced Chronic Neuropathy and Potentiates Its Antiproliferative Activity in Mice.

Oxaliplatin, the first-line chemotherapeutic agent against colorectal cancer (CRC), induces peripheral neuropathies, which can lead to dose limitation and treatment discontinuation. Downregulation of potassium channels, which involves histone deacetylase (HDAC) activity, has been identified as an important tuner of acute oxaliplatin-induced hypersensitivity. MS-275, a class I histone deacetylase inhibitor (HDACi), prevents acute oxaliplatin-induced peripheral neuropathy (OIPN). Moreover, MS-275 exerts anti-tumor activity in several types of cancers, including CRC. We thus hypothesized that MS-275 could exert both a preventive effect against OIPN and potentially a synergistic effect combined with oxaliplatin against CRC development. We first used RNAseq to assess transcriptional changes occurring in DRG neurons from mice treated by repeated injection of oxaliplatin. Moreover, we assessed the effects of MS-275 on chronic oxaliplatin-induced peripheral neuropathy development in vivo on APCMin/+ mice and on cancer progression when combined with oxaliplatin, both in vivo on APCMin/+ mice and in a mouse model of an orthotopic allograft of the CT26 cell line as well as in vitro in T84 and HT29 human CRC cell lines. We found 741 differentially expressed genes (DEGs) between oxaliplatin- and vehicle-treated animals. While acute OIPN is known as a channelopathy involving HDAC activity, chronic OIPN exerts weak ion channel transcriptional changes and no HDAC expression changes in peripheral neurons from OIPN mice. However, MS-275 prevents the development of sensory neuropathic symptoms induced by repeated oxaliplatin administration in APCMin/+ mice. Moreover, combined with oxaliplatin, MS-275 also exerts synergistic antiproliferative and increased survival effects in CT26-bearing mice. Consistently, combined drug associations exert synergic apoptotic and cell death effects in both T84 and HT29 human CRC cell lines. Our results strongly suggest combining oxaliplatin and MS-275 administration in CRC patients in order to potentiate the antiproliferative action of chemotherapy, while preventing its neurotoxic effect.

Behavioral and immunohistological assessment of painful neuropathy induced by a single oxaliplatin injection in the rat.

In clinical use, a single infusion of oxaliplatin, widely used to treat metastatic colorectal cancer, induces specific sensory neurotoxicity signs triggered or aggravated by exposure to cold. To study the pathophysiology of these symptoms, we developed and characterized an animal model that reproduces the effects of a single intraperitoneal oxaliplatin administration (3, 6 and 12 mg/kg). Significant allodynia and hyperalgesia to cold stimuli were rapidly observed from 24 h to day 5 with a maximum lowering of 76% at t+30 h versus control. Other behavioral assessments revealed rapid persistent mechanical allodynia, but no thermal hyperalgesia or allodynia to heat and no hyperalgesia to mechanical stimuli. An immunohistochemical study in the superficial layers of the spinal dorsal horn revealed a marked increase in substance P immunoreactivity versus controls (12% versus 4%), whereas calcitonin gene-related peptide (CGRP) immunoreactivity was unchanged. This new animal model for the first time closely mimics the effects observed in humans after a single oxaliplatin infusion, especially onset and highly intense sensory disturbances, hypersensitivity to cold with allodynia and hyperalgesia signs. This model may help to elucidate the mechanisms of this thermal hypersensitivity, especially the possible involvement of small-diameter A-fibers in cold allodynia symptoms. These selective effects may clue up the mechanistic basis for the acute oxaliplatin neuropathy leading to a better understanding of the clinical condition and to optimize its treatment.

Evidence for an exclusive antinociceptive effect of nociceptin/orphanin FQ, an endogenous ligand for the ORL1 receptor, in two animal models of neuropathic pain.

Nociceptin/orphanin FQ (noci/OFQ), the endogenous ligand for the orphan ORL1 (opioid receptor-like1), has been shown to be anti- or pronociceptive and modify morphine analgesia in rats after central administration. We comparatively examined the effect of noci/OFQ on hyperalgesia and morphine analgesia in two experimental models of neuropathic pain: diabetic (D) and mononeuropathic (MN) rats. Noci/OFQ, when intrathecally (i.t.) injected (0.1, 0.3, or 1, to 10 microg/rat) was ineffective in normal rats, but reduced and suppressed mechanical hyperalgesia (paw-pressure test) in D and MN rats, respectively. This spinal inhibitory effect was suppressed by naloxone (10 microg/rat, i.t.) in both models. Combinations of systemic morphine with spinal noci/OFQ resulted in a strong potentiation of analgesia in D rats. In MN rats, an isobolographic analysis showed that the morphine+noci/OFQ association (i.t.) suppressed mechanical hyperalgesia in a superadditive manner. In summary, the present findings reveal that spinal noci/OFQ produces a differential antinociception in diabetic and traumatic neuropathic pain according to the etiology of neuropathy, an effect possibly mediated by opioid receptors. Moreover, noci/OFQ combined with morphine produces antinociceptive synergy in experimental neuropathy, opening new opportunities in the treatment of neuropathic pain.

Antihyperalgesic effect of levetiracetam in neuropathic pain models in rats.

The purpose of this study was to assess, in rats, the antinociceptive effects of levetiracetam (i.p.), a novel antiepileptic drug, in acute pain tests and in two models of human neuropathic pain. Levetiracetam and carbamazepine contrasted morphine by an absence of effect in the tail flick and hot plate tests. In normal rats, carbamazepine failed to modify the vocalisation thresholds to paw pressure whereas levetiracetam slightly increased this threshold only at the highest dose (540 mg/kg) for 30 min. In the sciatic nerve with chronic constriction injury model, the highest dose of levetiracetam (540 mg/kg) and carbamazepine (30 mg/kg) reversed the hyperalgesia. In streptozocin-induced diabetic rats, levetiracetam dose-dependently increased the vocalization threshold from 17 to 120 mg/kg reaching a similar effect as 10 mg/kg of carbamazepine. These results indicate that levetiracetam induces an antihyperalgesic effect in two models of human neuropathic pain, suggesting a therapeutic potential in neuropathic pain patients.

Involvement of N-methyl-D-aspartate receptors in nociception in the cyclophosphamide-induced vesical pain model in the conscious rat.

We previously showed that the intraperitoneal (i.p.) administration of 200mg/kg cyclophosphamide, an antitumoral agent, modified the behaviour of rats with cystitis induced by acrolein, a toxic urinary by-product of cyclophosphamide. This behaviour, (namely decreased breathing rate, closing of the eyes, and specific postures), was scored to indirectly assess the nociception elicited by the cystitis and to use this experimental model as a vesical pain model. Here we investigated the involvement of the N-methyl-D-aspartate (NMDA) receptors and thus of the excitatory amino acid system in this model. We administered dizocilpine (0.01 to 0.1mg/kg intravenously (i.v.) and 1 to 20 microg/rat intrathecally (i.t.)) and ketamine (5 and 10mg/kg i.v. and 50 to 1000 microg/rat i.t.), two non-competitive NMDA receptor antagonists that bind to the channel site, and AP-5 (0.01 to 1mg/kg i.v. and 20 to 500 microg/rat i.t), a competitive antagonist that binds to the glutamate site. Whichever the route of administration (i.v. or i.t.), dizocilpine dose-relatedly reduced the behavioural disorders induced by cyclophosphamide. Systemic ketamine also dose-dependently, though transiently, reduced the effects of cyclophosphamide, but ketamine i.t. and AP-5 i.v. and i.t. did not induce any reduction of these effects.These results (i) demonstrate that in the cyclophosphamide-induced vesical pain model NMDA receptors are involved in the nociception, as shown by the effects of dizocilpine and systemic ketamine, (ii) reveal marked differences in the data obtained with various NMDA receptor antagonists, possibly due to their physicochemical properties, to the animal pain model used, to the noxious stimulus applied or to any combination of these factors.

Spinal effect of the cholecystokinin-B receptor antagonist CI-988 on hyperalgesia, allodynia and morphine-induced analgesia in diabetic and mononeuropathic rats.

Since evidence points to the involvement of cholecystokinin (CCK) in nociception, we examined the effect of intrathecal CI-988, an antagonist of the CCK-B receptors, on mechanical hyperalgesia and allodynia in normal, mononeuropathic and diabetic rats,. Owing to the anti-opioid activity of CCK, it has been suggested that hyperactivity in the spinal CCK system is responsible for the low sensitivity of neuropathic pain to opioids. We therefore also evaluated the effect of the combination of i.t. CI-988 + i.v. morphine on mechanical hyperalgesia in diabetic and mononeuropathic rats using isobolographic analysis. Although ineffective in normal rats, CI-988 induced antinociceptive effects in diabetic (290 +/- 20 g with a cut-off of 750 g) and mononeuropathic (117 +/- 16 g; cut-off 750 g) rats, suggesting an involvement of the CCKergic system in neurogenic pain conditions. The combination of CI-988 and morphine showed a superadditive interaction in the diabetic rats only (477 +/- 16 g; cut-off 750 g), in comparison with the antinociceptive effect of each drug. In addition, CI-988 exhibited a weak anti-allodynic effect in mononeuropathic rats, and no anti-allodynic effect in diabetic rats. These results show the CCK-B receptor blockade-mediated antinociceptive effects and reveals the antinociceptive action of morphine in diabetic rats after CCKergic system inhibition.